1. Field of the Invention
The present invention relates to a disk playback apparatus and a disk playback method for performing a playback operation of, for example, digital versatile disks (DVDs).
2. Description of the Related Art
DVDs are receiving widespread attention as disc recording media. A DVD has a diameter of 12 cm and a thickness of 1.2 mm, which are the same dimensions as a compact disc (CD). However, a DVD achieves a greater recording capacity than a CD, such as 4.7 GB for a single layer and 8.5 GB for double layers, by increasing the recording density.
A mixture of various types of data can be stored in a DVD using image data compression techniques, such as MPEG2 or audio data compression techniques, and control data for implementing various functions also can be stored in the DVD. When, for example, a movie is recorded on a DVD, video data and audio data are normally stored. However, in addition to the video data and the audio data, other types of data, for example, subtitle data including a plurality of languages, can be stored so that a user is able to select and display a desired language.
In most DVD playback apparatuses, when playing back a movie recorded on a DVD, the movie can be played back at a speed greater than normal speed, such as from 2× to 30×, by entering a fast-forward or a fast-rewind instruction, so as to locate a desired playback position. Playback operations at various speeds are implemented as follows. When the playback speed is lower, the same number of images (for example, 60/second) as that at the normal playback speed are decoded, and the images are produced by reducing the number of images according to the playback speed. When the playback speed is higher, video object units (VOBUs), which are predetermined playback units, are sparsely extracted and are played back.
In known disk playback apparatuses, when video and sound of, for example, a movie, are played back at a greater playback speed (for example, 2× or higher) while displaying the subtitles, the decoding operation cannot keep up with the playback operation, and thus, the subtitles cannot be displayed in a scene in which the subtitles should normally be displayed. Accordingly, when searching for a desired playback position by performing a fast-forward or a fast-rewind operation, the user cannot locate the desired position while checking the content of the subtitles. It is difficult to locate a playback position, for example, in scenes in which only the words (speech) change with very little change in the images. In this case, the ease of operation is substantially reduced.
Also in known disk playback apparatuses, when the playback speed is returned to the normal playback speed from a speed greater than normal, the subtitles when the normal playback speed is resumed sometimes cannot be displayed, and the subtitles normally start at a subsequent playback position. In this case, the user must wait until the subtitles are subsequently displayed or must perform a playback operation once again at a speed greater than normal to locate the playback position. The playback position cannot be located by checking the subtitles without performing the above-described complicated operation.